Pregnancy Week Calculator
How to Calculate How Many Weeks Pregnant You Are
Calculating your pregnancy progress is usually done using the Last Menstrual Period (LMP) method. This is the standard practice used by healthcare providers worldwide. Because it is often difficult to know the exact date of conception, doctors use the first day of your last period as "Day 1" of your 40-week pregnancy journey.
The Pregnancy Calculation Formula
The math behind determining your weeks of pregnancy is straightforward. To calculate your current week, you count the number of days that have passed since the first day of your last period and divide by seven.
The Formula:
(Today's Date - LMP Date) / 7 = Weeks Pregnant
To find your Estimated Due Date (EDD), clinicians use Naegele's Rule: Add seven days to the first day of your LMP, subtract three months, and add one year. This equates to approximately 280 days from the LMP.
Calculation Example
If the first day of your last period was January 1st:
- LMP: January 1
- Today's Date: February 12
- Total Days: 42 days
- Calculation: 42 / 7 = 6 weeks
- Result: You are exactly 6 weeks pregnant.
Frequently Asked Questions
Why am I considered 4 weeks pregnant when I only conceived 2 weeks ago?
Pregnancy "weeks" start counting from your period, not from the moment sperm meets egg. During weeks 1 and 2, your body is actually preparing for ovulation. By the time you miss your period, you are technically 4 weeks along.
Does a long cycle change my due date?
Yes. Most calculators assume a 28-day cycle. If you have a 35-day cycle, you likely ovulated later, meaning your pregnancy might be "younger" than a standard LMP calculation suggests. Our calculator allows you to adjust for cycle length for better accuracy.
What are the trimesters?
– 1st Trimester: Weeks 1 to 12
– 2nd Trimester: Weeks 13 to 26
– 3rd Trimester: Week 27 to birth